System and method for reliable sensing of memory cells

ABSTRACT

Disclosed herein are related to a memory system including a memory cell and a circuit to operate the memory cell. In one aspect, the circuit includes a pair of transistors to electrically couple, to the bit line, a selected one of i) a voltage source to supply a reference voltage to the memory cell and ii a sensor to sense a current through the memory cell. In one aspect, the circuit includes a first transistor. The first transistor and the bit line may be electrically coupled between the pair of transistors and the memory cell in series.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. ProvisionalApplication No. 63/031,145, filed May 28, 2020, entitled “SYSTEMS ANDMETHODS FOR SWITCHING WL OF FLASH MEMORY”, which is incorporated hereinby reference in its entirety for all purposes.

BACKGROUND

Developments in electronic devices, such as computers, portable devices,smart phones, internet of thing (IoT) devices, etc., have promptedincreased demands for memory devices. In general, memory devices may bevolatile memory devices and non-volatile memory devices. Volatile memorydevices can store data while power is provided but may lose the storeddata once the power is shut off. Unlike volatile memory devices,non-volatile memory devices may retain data even after the power is shutoff but may be slower than the volatile memory devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a diagram of a memory system, in accordance with oneembodiment.

FIG. 2 is a bit line controller, in accordance with one embodiment.

FIG. 3 is a diagram of a switching circuit and a set of memory cellsconnected to the switching circuit, in accordance with one embodiment.

FIG. 4 is a timing diagram showing an operation of the memory system ofFIG. 1 , in accordance with one embodiment.

FIG. 5 is a diagram of a switching circuit and a feedback circuitconnected to the switching circuit, in accordance with one embodiment.

FIG. 6 is a diagram of a bias circuit to control the feedback circuit ofFIG. 5 , in accordance with one embodiment.

FIG. 7 is a diagram of a switching circuit and a feedback circuitconnected to the switching circuit, in accordance with one embodiment.

FIG. 8 is a diagram of a switching circuit and a set of resistive memorycells connected to the switching circuit, in accordance with oneembodiment.

FIG. 9 is a flowchart showing a method of configuring a memory cell, inaccordance with some embodiments.

FIG. 10 is an example block diagram of a computing system, in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In accordance with some embodiments, a memory system includes a memorycell and a memory controller to operate the memory cell. In one aspect,the memory controller includes a pair of transistors to electricallycouple, to the bit line, a selected one of: i) a voltage source to biasthe memory cell and ii) a sensor to sense a current through the memorycell. In one aspect, the memory controller includes a first transistor,where the first transistor and the bit line are connected between thepair of transistors and the memory cell in series. In one aspect, thepair of transistors includes a second transistor connected between thevoltage source and the memory cell, and a third transistor connectedbetween the sensor and the memory cell.

In one aspect, the memory controller generates various pulses toconfigure the memory cell. For example, the memory controller generatesa first pulse and applies the first pulse to a word line of a memorycell. The memory controller may also generate a set of second pulses andapply the set of second pulses to the second transistor of the pair oftransistors. The memory controller may generate a set of third pulsesand apply the set of third pulses to the third transistor of the pair oftransistors. In one aspect, one of the set of second pulses has a firststate during a first duration (or a set time period) after a first time,at which an edge (e.g., rising edge) of the first pulse occurs, toelectrically couple the voltage source to the bit line. During the firstduration (or the set time period), one of the set of third pulses has asecond state to electrically decouple the sensor from the bit line.After the first duration, the set of second pulses and the set of thirdpulses may have opposite phases during a second duration, such that thepair of transistors can be switched or toggled differentially.

Advantageously, the disclosed memory system can perform high speedoperations on one or more memory cells with improved accuracy. In oneaspect, writing data at memory cells or reading data from the memorycells includes applying various high-speed pulses (e.g., over 1 GHz) tothe memory cells. For example, a pulse may be applied to a word line (ora gate line) connected to a memory cell. However, due to parasiticcapacitances among a word line and other gate lines, the first pulseapplied to the word line may affect a voltage or current at other gatelines. Change in voltage or current at other gate lines due to parasiticcapacitances may cause inaccuracy in reading data stored by a memorycell. In one approach, in response to an edge (e.g., rising edge) of thefirst pulse applied to the word line, the disclosed memory system mayelectrically couple the bit line to the voltage source whileelectrically decoupling the bit line from the sensor for the firstduration (or a set time period) to allow voltages or currents at othergate lines to settle. After the first duration (or the set time period),the disclosed memory system may electrically decouple the bit line fromthe voltage source while electrically coupling the bit line to thesensor to sense or read data stored by the memory cell. By reading datastored by the memory cell after the voltages or currents at other gatelines settle, data stored by the memory cell can be read in a reliablemanner with reduced effects due to parasitic capacitances.

In one aspect, an edge (e.g., falling edge) of the first pulse appliedto the word line is aligned with an edge (e.g., rising edge) of anotherone of the set of second pulses and an edge (e.g., falling edge) ofanother one of the set of third pulses. In one aspect, in response tothe edge (e.g., falling edge) of the first pulse, the memory cell may bedisabled. By aligning the edge (e.g., falling edge) of the first pulsewith the edge (e.g., rising edge) of the another one of the set ofsecond pulses and the edge (e.g., falling edge) of the another one ofthe set of third pulses, the pair of transistors may electrically couplethe voltage source to the bit line and electrically decouple the memorycell from the bit line when the memory cell is disabled, such that afluctuation or variation in a voltage at the bit line can be reduced.

FIG. 1 is a diagram of a memory system 100, in accordance with oneembodiment. In some embodiments, the memory system 100 is implemented asan integrated circuit. In some embodiments, the memory system 100includes a memory controller 105 and a memory array 120. The memoryarray 120 may include a plurality of storage circuits or memory cells125 arranged in two- or three-dimensional arrays. Each memory cell 125may be connected to a corresponding gate line GL and a corresponding bitline BL. Each gate line may include any conductive material. The memorycontroller 105 may write data to or read data from the memory array 120according to electrical signals through gate lines GL and bit lines BL.In other embodiments, the memory system 100 includes more, fewer, ordifferent components than shown in FIG. 1 .

The memory array 120 is a hardware component that stores data. In oneaspect, the memory array 120 is embodied as a semiconductor memorydevice. The memory array 120 includes a plurality of storage circuits ormemory cells 125. In some embodiments, the memory array 120 includesgate lines GL1, GL2 . . . GLJ, each extending in a first direction(e.g., X-direction) and bit lines BL1, BL2 . . . BLN, each extending ina second direction (e.g., Y-direction). The gate lines GL and the bitlines BL may be conductive metals or conductive rails. In one aspect,each memory cell 125 is connected to a corresponding gate line GL and acorresponding bit line BL, and can be operated according to voltages orcurrents through the corresponding gate line GL and the correspondingbit line BL. In one aspect, each memory cell 125 includes a flash memorycell with at least two gate electrodes. In some embodiments, the memoryarray 120 includes additional lines (e.g., select lines, referencelines, reference control lines, power rails, etc.).

The memory controller 105 is a hardware component that controlsoperations of the memory array 120. In some embodiments, the memorycontroller 105 includes a bit line controller 112, a gate linecontroller 114, and a timing controller 110. In one configuration, thegate line controller 114 is a circuit that provides a voltage or acurrent through one or more gate lines GL of the memory array 120, andthe bit line controller 112 is a circuit that provides or senses avoltage or current through one or more bit lines BL of the memory array120. In one configuration, the timing controller 110 is a circuit thatprovides control signals or clock signals to the gate line controller114 and the bit line controller 112 to synchronize operations of the bitline controller 112 and the gate line controller 114. The bit linecontroller 112 may be connected to bit lines BL of the memory array 120,and the gate line controller 114 may be connected to gate lines GL ofthe memory array 120. In one example, to write data to a memory cell125, the gate line controller 114 applies a voltage or current to thememory cell 125 through a gate line GL connected to the memory cell 125,and the bit line controller 112 applies a voltage or currentcorresponding to data to be stored to the memory cell 125 through a bitline BL connected to the memory cell 125. In one example, to read datafrom a memory cell 125, the gate line controller 114 provides a voltageor a current to the memory cell 125 through a gate line GL connected tothe memory cell 125, and the bit line controller 112 senses a voltage ora current corresponding to data stored by the memory cell 125 through abit line BL connected to the memory cell 125. In some embodiments, thememory controller 105 includes more, fewer, or different components thanshown in FIG. 1 .

FIG. 2 is a diagram of the bit line controller 112 of FIG. 1 , inaccordance with one embodiment. In some embodiments, the bit linecontroller 112 includes a voltage source 210, current sensors 220A, 220B. . . 220N, a bias controller 230, and switching circuits 240A, 240B . .. 240N. These components may operate together to apply a voltage orcurrent to the memory cell 125, and sense current Iout through one ormore memory cells 125 to read data stored by the memory cell 125. Insome embodiments, the bit line controller 112 includes more, fewer, ordifferent components than shown in FIG. 2 .

In one aspect, the voltage source 210 is a component that provides areference voltage Vref to the switching circuits 240A, 240B . . . 240N.In some embodiments, the voltage source 210 is replaced by othercomponents that perform the similar functionalities of the voltagesource 210 described herein. In one configuration, the voltage source210 is connected to the switching circuits 240A, 240B . . . 240N throughconductive traces or metal rails. In this configuration, the voltagesource 210 may generate a reference voltage Vref and provide thereference voltage Vref to the switching circuits 240A, 240B . . . 240N.The reference voltage Vref may be a supply voltage VDD or any voltage tosupply to the bit line BL. In some embodiments, the voltage source 210is implemented as a separate component from the bit line controller 112.

In one aspect, each current sensor 220 is a component that sensescurrent Iout (currents Iout A, Iout B . . . Iout N) from or through acorresponding switching circuit 240. In some embodiments, the currentsensor 220 is replaced by other components that perform the similarfunctionalities of the current sensor 220 described herein. In oneconfiguration, each of the current sensors 220A . . . 220N is connectedto a corresponding one of the switching circuits 240A, 240B . . . 240Nthrough conductive traces or metal rails. In this configuration, eachcurrent sensor 220 may sense current Tout through the correspondingswitching circuit 240. In some embodiments, the current sensor 220includes a capacitor connected to the switching circuit 240 and a senseamplifier connected to the capacitor. In one approach, the currentsensor 220 may charge the capacitor, such that the capacitor has aninitial voltage. According to the current Tout through the switchingcircuit 240, the capacitor may discharge, such that the voltage at thecapacitor may decrease from the initial voltage. The sense amplifier maydetect or sense the voltage at the capacitor corresponding to thecurrent Tout through the switching circuit to determine the data storedby the memory cells. In some embodiments, the current sensors 220A . . .220N are implemented as separate components from the bit line controller112.

In one aspect, the switching circuit 240 is a component that selectivelycouples the voltage source 210 or the current sensor 220 to a bit lineBL. The switching circuit 240 may be embodied as a pair of transistors.Each transistor may be metal oxide semiconductor field effect transistor(MOSFET), FinFET, gate all around FET (GAAFET), or any transistor. Inone configuration, the switching circuit 240 includes a first portconnected to the voltage source 210, a second port connected to thecurrent sensor 220, and a third port connected to a corresponding bitline BL. The switching circuit 240 may also include a control portconnected to the timing controller 110 to receive control signals orpulses from the timing controller 110. In this configuration, theswitching circuit 240 may receive control signals or pulses from thetiming controller 110, and electrically couple a selected one of: thevoltage source 210 and the current sensor 220 to the bit line BL,according to the control signals or pulses.

In one aspect, the bias controller 230 is a component that controls orbiases voltages at the bit lines. The bias controller 230 may beembodied as a feedback circuit that senses a voltage at a bit line BLand generates a bias voltage VBias according to the sensed voltage atthe bit line BL. The bias controller 230 may apply the bias voltageVBias to the switching circuit 240. In one aspect, the bias controller230 may regulate the voltage at the bit line BL to be withinpredetermined range (e.g., ±50 mV) to allow stable operations of thememory cell 125.

FIG. 3 is a diagram of the switching circuit 240 and a set of memorycells M1, M2 . . . Mn, in accordance with one embodiment. In someembodiments, the switching circuit 240 includes a first transistor I1,and a pair of transistors I2, I3. In one aspect, the switching circuit240 is configured to provide a reference voltage Vref to one or more ofthe set of memory cells M1, M2 . . . Mn through the a bit line BL orallow current Iout through one or more of the set of memory cells M1, M2. . . Mn.

Each memory cell M may be the memory cell 125. The memory cell M may bea flash memory cell with at least two gate electrodes, a drain electrodeconnected to a bit line BL, and a source electrode connected to a powerrail for providing a supply voltage (e.g., GND or VSS) or a select line.In one example, the memory cell M includes a split gate electrode SG, acontrol gate electrode CG, and an erase gate electrode EG connected togate line controller 114. The split gate electrodes SG of differentmemory cells may be connected to the gate line controller 114 throughcorresponding word lines. To perform operations on the memory cell M,various voltages can be applied to the gate electrodes. In one aspect,operations on the memory cell M can be performed according to a voltageapplied to the split gate electrode SG and a threshold voltage of thememory cell M, where the threshold voltage of the memory cell M may bedetermined according to a difference between a voltage at the controlgate electrode CG and a voltage at the erase gate electrode EG of thememory cell M. For example, to store data, 1V, 8V and 4V can be appliedto the gate electrodes SG, CG, EG, respectively. For example, to readdata, 1.1V, 0.8V and 0V can be applied to the gate electrodes SG, CG,EG, respectively. For another example, to erase data, 0V, 0V and 8V canbe applied to the gate electrodes SG, CG, EG, respectively.

In some embodiments, the switching circuit 240 includes the transistorsI1, I2, I3 having a differential architecture. The transistors I1, I2,I3 may be embodied as MOSFET, FinFETs, GAAFETs, or any transistors. Thetransistors I1, I2, I3 may be N-type transistors. In one configuration,the first transistor I1 includes a source electrode connected to the bitline BL, a gate electrode connected to the bias controller 230, and adrain electrode connected to source electrodes of the transistors I2,I3. In one configuration, the second transistor I2 includes the sourceelectrode connected to a drain electrode of the first transistor I1 andthe source electrode of the third transistor I3. The second transistorI2 also includes a gate electrode connected to the timing controller110, and a drain electrode connected to the voltage source 210 through apower rail. The third transistor I3 also includes a gate electrodeconnected to the timing controller 110, and a drain electrode connectedto the current sensor 220 through a metal rail.

In this configuration, the switching circuit 240 provides the referencevoltage Vref to the bit line BL or enables current Iout through the bitline BL. In some embodiments, the switching circuit 240 includesdifferent components than shown in FIG. 3 , or replaced by othercomponents performing the functionality of the switching circuit 240described herein. In one aspect, the first transistor I1 may receive abias voltage VBias from the bias controller 230 at the gate electrode.The first transistor I1 may operate as a cascode transistor to improveresistance or impedance at the bit line BL, and improve stability ofvoltage or current at the bit line BL according to the bias voltageVBias. The second transistor I2 may receive a signal SW1 including oneor more pulses from the timing controller 110 at the gate electrode andreceive a reference voltage Vref from the voltage source 210 at thedrain electrode. The third transistor I3 may receive a signal SW2including one or more pulses from the timing controller 110 at the gateelectrode. According to a high voltage (e.g., VDD) of the signal SW1,the transistor I2 may electrically couple the voltage source 210 to thedrain electrode of the transistor I1 to provide the reference voltageVref to the drain electrode of the transistor I1. According to a lowvoltage (e.g., GND) of the signal SW1, the transistor I2 mayelectrically decouple the voltage source 210 from the drain electrode ofthe transistor I1. According to a high voltage (e.g., VDD) of the signalSW2, the transistor I3 may electrically couple a capacitor C of thecurrent sensor 220 to the drain electrode of the transistor I1.According to a low voltage (e.g., GND) of the signal SW2, the transistorI3 may electrically decouple the current sensor 220 from the drainelectrode of the transistor I1. Hence, the switching circuit 240 mayprovide the reference voltage Vref to the bit line BL or enable currentIout through the set of memory cells M1, M2 . . . Mn to read data storedby the set of memory cells M1, M2 . . . Mn, according to the signalsSW1, SW2.

In one aspect, the timing controller 110 can apply signals SW1, SW2 tothe switching circuit 240 and the gate line controller 114 can applyword line control signals WL to respective split gate electrodes of thememory cells M1 . . . Mn in a coordinated manner to read data stored bythe memory cells M1 . . . Mn. In one approach, any one of: the signalSW2 having a low voltage (e.g., GND) applied to the switching circuit240 and the word line control signal WL having a low voltage (e.g., GND)applied to the split gate electrode SG of the memory cell M may preventcurrent Tout to flow from the capacitor C through the bit line BL. Inone approach, the signal SW2 having a high voltage (e.g., VDD) and theword line control signal WL having a high voltage (e.g., VDD) may allowcurrent Tout to flow from the capacitor C through the bit line BL. Thecurrent sensor 220 may sense a voltage at the capacitor C in response tothe current Tout through the bit line BL to determine data stored by thememory cells M1 . . . Mn. In one aspect, the signals SW1, SW2, and wordline control signals (or various pulses) can be applied to the switchingcircuit 240 and the set of memory cells M1 . . . Mn in a coordinatemanner, such that high speed read operations (e.g., over 1 Gbps) can beperformed in a reliable manner, as described below with respect to FIG.4 .

FIG. 4 is a timing diagram 400 showing an operation of the memory system100 of FIG. 1 , in accordance with one embodiment. In one aspect, thetiming controller 110 generates signals SW1, SW2 including pulses, andapplies the signals SW1, SW2 to the gate electrodes of the transistorsI2, I3. The timing controller 110 may configure or cause the gate linecontroller 114 to generate word line control signals WL[1] . . . WL[n],and apply the word line control signals WL[1] . . . WL[n] to split gateelectrodes of the memory cells M1 . . . Mn. In one example, a word linecontrol signal WL[1] having a high voltage (e.g., VDD) may enable thememory cell M1 to conduct current according to data stored by the memorycell M1. In one aspect, the word line control signal WL[1] having a lowvoltage (e.g., GND) may disable the memory cell M1 from conductingcurrent.

In some embodiments, the timing controller 110 generates the signal SW1having a low voltage (e.g., GND) and the signal SW2 having a highvoltage (e.g., VDD) for a set time period T1, from a time at whichrising edges of the word line control signals WL[1] . . . WL[n] occur.In one aspect, the word line control signals WL[1] . . . WL[n] havepulses at a high frequency (e.g., over 1 GHz or higher). Such highfrequency pulses may be coupled to or propagate to other gate lines ofthe memory cells through parasitic capacitances. The set time period T1may be larger than a time period (e.g., 2˜3 ns) for voltages or currentat the gate lines to settle after parasitic coupling. By applying thesignal SW1 having a high voltage (e.g., VDD) and the signal SW2 having alow voltage (e.g., GND) to the switching circuit 240 for the set timeperiod T1, the switching circuit 240 may provide the reference voltageVref to the bit line BL and disable current Iout from flowing throughthe bit line BL until the voltages or current at the gate lines settleafter the parasitic couplings.

After the set time period T1, the timing controller 110 may generate thesignals SW1, SW2 having pulses to read data stored by the memory cellsM1 . . . Mn. The pulses of the SW1, SW2 may have a sampling period Tswith opposite phases. In one aspect, by applying the signal SW1 having alow voltage (e.g., GND) and the signal SW2 having a high voltage (e.g.,VDD) to the switching circuit 240, the switching circuit 240 may notprovide the reference voltage Vref to the bit line BL and enable currentIout corresponding to data stored by the memory cells M1 . . . Mn toflow through the bit line BL. For example, a voltage Vout at thecapacitor C of the current sensor 220 may decrease after the set timeperiod T1 according to the current Iout through the bit line BL and theswitching circuit 240. The sense amplifier of the current sensor 220 maysense the decreased voltage at the capacitor C, and determine datastored by the memory cells M1 . . . Mn, according to the amount ofdecrease in the voltage at the capacitor C. By sensing current after theset time period T1, data stored by the memory cells M1 . . . Mn can besensed or read in an accurate manner despite parasitic couplings.

In one aspect, a falling edge of the signal WL applied to the split gateelectrode SG of the memory cell M through the word line is aligned witha rising edge of the signal SW1 and a falling edge of the signal SW2applied to the switching circuit 240. In one aspect, in response to thefalling edge of the signal WL, the memory cell M may be disabled fromconducting current. By aligning the falling edge of the signal WL withthe rising edge of the signal SW1 and the falling edge of the signal SW2applied to the switching circuit 240, the switching circuit 240 mayelectrically couple the voltage source 210 to the bit line BL andelectrically decouple the current sensor 220 from the bit line BL whenthe memory cell M is disabled, such that a fluctuation or variation in avoltage at the bit line BL, for example, due to the falling edge of thesignal WL through parasitic capacitances can be reduced.

FIG. 5 is a diagram of the switching circuit 240 and a feedback circuit510 connected to the switching circuit 240, in accordance with oneembodiment. In one aspect, the feedback circuit 510 is part of the biascontroller 230. In some embodiments, the feedback circuit 510 includesan input port connected to the bit line BL (or a source electrode of thetransistor I1 of the switching circuit 240) and an output port coupledto a gate electrode of the transistor I1. In this configuration, thefeedback circuit 510 may sense a voltage at the bit line BL, andgenerate a bias voltage VBias according to the sensed voltage toregulate or control voltage at the bit line BL.

In some embodiments, the feedback circuit 510 includes a transistor I4and a transistor I5. The transistors I4, I5 may be MOSFETs, FinFETs,GAAFETs or any transistors. The transistor I4 may be a N-type transistorand the transistor I5 may be a P-type transistor. In one configuration,a source electrode of the transistor I4 is connected to a power rail, atwhich a ground voltage (e.g., GND) is provided. In one configuration, agate electrode of the transistor I4 is connected to the bit line BL. Inone configuration, a drain electrode of the transistor I4 is connectedto a drain electrode of the transistor I5 and a gate electrode of thetransistor I1. In one configuration, a gate electrode of the transistorI5 receives a voltage control signal Vctrl. In one configuration, asource electrode of the transistor I5 is connected to a power rail, atwhich a supply voltage (e.g., VDD) is provided. In this configuration,the transistor I4 may sense a voltage at the bit line BL, and generate abias voltage VBias at the drain electrode of the transistor I4,according to the sensed voltage. For example, in response to a decreasein the voltage at the bit line BL, the transistor I4 may increase thebias voltage VBias, thereby causing the voltage at the bit line BL toincrease. For example, in response to an increase in the voltage at thebit line BL, the transistor I4 may decrease the bias voltage VBias,thereby causing the voltage at the bit line BL to decrease.

In one aspect, the control voltage Vctrl can set a current (e.g., DCcurrent) through the transistors I4, I5. According to the currentthrough the transistors I4 and I5 according to the control voltageVctrl, the bias voltage VBias can be set. In one aspect, the currentthrough the transistors I4, I5 can set a transconductance (gm) or anamount of responsiveness of the transistor I4 to the voltage at the bitline BL. Hence, the feedback circuit 510 can be adaptively adjusted orconfigured according to the control voltage Vctrl.

FIG. 6 is a diagram of a bias circuit 600 to control the feedbackcircuit 510 of FIG. 5 , in accordance with one embodiment. In someembodiments, the bias circuit 600 includes transistors Ib1, Ib2, Ib3,Ib4, memory cells Mb0, Mb1, an amplifier 620, and temperature control(TC) regulated current source 610. The transistors Ib1, Ib2, Ib3, Ib4may be MOSFETs, FinFETs, GAAFETs or any transistors. The transistorsIb1, Ib2, Ib3 may be N-type transistors and the transistor Ib4 may be aP-type transistor. The temperature coefficient regulated current source610 may be a bandgap circuit or any circuit that provides a controlledor regulated current over a temperature range (e.g., −40° C. to 150°C.). The memory cells Mb0, Mb1 may be same type of memory cells (e.g.,flash memory cells) as the memory cells M1 . . . Mn. These componentsmay operate together to generate the control voltage Vctrl and providethe control voltage Vctrl to the feedback circuit 510.

In one configuration, the TC regulated current source 610 is connectedto a first input port (e.g., “+” input port) of the amplifier 620, andthe memory cell Mb0. In one configuration, a second input port (e.g.,“+” input port) of the amplifier 620 is connected to a gate electrode ofthe transistor Ib4 to form a negative feedback configuration to generatethe control signal Vctrl at the output port. In one configuration, theoutput port of the amplifier 620 is connected to a gate electrode of thetransistor Ib4. The amplifier 620 may compare a voltage at the firstinput port and a voltage at the second input port, and generate oradjust the control voltage Vctrl at the output port to reduce thedifference between a voltage at the first input port and a voltage atthe second input port. In one aspect, the transistors Ib4, Ib3, Ib1, Ib2and the memory cell Mb1 can emulate or mimic the transistors I4, I3, I1,I2 (or I3) and the memory cell M. By implementing the transistors Ib4,Ib3, Ib1, Ib2 and the memory cell Mb1 having the similar configurationas the transistors I4, I3, I1, I2 (or I3) and the memory cell M, theamplifier 620 may generate the control voltage Vctrl for controllingcurrent through the transistors I4, I5 of the feedback circuit 510despite temperature variations.

FIG. 7 is a diagram of the switching circuit 240 and a feedback circuit710 connected to the switching circuit 240, in accordance with oneembodiment. In one aspect, the feedback circuit 710 is part of the biascontroller 230. In some embodiments, the feedback circuit 710 may beimplemented instead of the feedback circuit 510. The feedback circuit710 may be embodied as an amplifier (e.g., operational amplifier). Inone configuration, the feedback circuit 710 includes a first input portto receive the control voltage Vctrl, a second input port connected tothe bit line BL, and an output port coupled to the gate electrode of thetransistor I1. In this configuration, the feedback circuit 710 maycompare the control voltage Vctrl at the first input port and thevoltage at the bit line BL, and generate or adjust the bias voltageVBias at the output port to reduce the difference between the controlvoltage Vctrl and the voltage at the bit line BL. In one aspect, thefeedback circuit 710 or operational amplifier implemented as shown inFIG. 7 can increase a loop gain of the feedback formed by the feedbackcircuit 710 and the transistor I1 to reduce variations or fluctuationsat the bit line BL.

FIG. 8 is a diagram of the switching circuit 240 and a set of resistivememory cells MR1, MR2 . . . MRn connected to the switching circuit 240,in accordance with one embodiment. In some embodiments, the set ofmemory cells MR1, MR2 . . . MRn may be implemented as the memory cells125 of FIG. 1 . Each memory cell MR may include a resistive memorydevice (resistive memory devices R1, R2 . . . Rn) (e.g., RRAM, PCRAM,MRAM device), and a transistor IM (transistors IM1, IM2 . . . IMn). Inone aspect, a transistor IM may be connected to a correspondingresistive memory device in series, and enable current to flow throughthe resistive memory device according to a word line control signal(word line control signals WL[1], WL[2] . . . WL[n]) provided through aword line. By enabling or disabling a current through the resistivememory device, the resistive memory device may store data. In oneaspect, the switching circuit 240 may selectively apply the referencevoltage Vref to the bit line BL or enable the current Iout to flowthrough memory cells MR1 . . . MRn, as described above with respect toFIG. 2 through 7 .

FIG. 9 is a flowchart showing a method 900 of reading data stored by thememory cell 125 by configuring the switching circuit 240, in accordancewith some embodiments. The method 900 may be performed by the memorycontroller 105 of FIG. 1 . In some embodiments, the method 900 isperformed by other entities. In some embodiments, the method 900includes more, fewer, or different operations than shown in FIG. 9 .

In an operation 910, the memory controller 105 applies a first pulse toa word line coupled to the memory cell M. The first pulse may be a pulseof a word line control signal. The memory cell M may be a flash memorycell, a resistive memory cell, or any memory cell for storing data. Inone approach, the timing controller 110 configures or causes the gateline controller 114 to apply the first pulse to the word line. In oneapproach, the timing controller 110 generates the signal SW1 having alow voltage (e.g., GND) and the signal SW2 having a high voltage (e.g.,VDD) for a set time period T1, from a time at which a rising edge of theword line control signal occurs.

In an operation 920, the memory controller 105 applies a referencevoltage Vref to the bit line BL for a set time period T1. In one aspect,the timing controller 110 applies a signal SW1 having a high voltage(e.g., VDD) to the transistor I2 of the switching circuit 240 and asignal SW2 having a low voltage (e.g., GND) to the transistor I3 of theswitching circuit 240. In response to the signal SW1 having the highvoltage and the signal SW2 having the low voltage, the transistor I2 maybe enabled and the transistor I3 may be disabled to electrically couplethe voltage source 210 to the bit line BL and electrically decouple thecurrent sensor 220 from the bit line BL. In one aspect, the first pulseapplied to a word line may affect voltages or current at other gatelines of the memory cell through parasitic coupling. The set time periodT1 may be larger than a time period (e.g., 2˜3 ns) for voltages orcurrent at the gate lines to settle after parasitic coupling between thegate lines and the word line. By applying the reference voltage Vref tothe bit line BL during the set time period, the voltage at the bit linecan be maintained or controlled reliably despite the parasiticcouplings.

In an operation 930, the memory controller 105 senses the current Toutthrough the memory cells after the set time period T1. In one approach,the timing controller 110 applies the signal SW1 having a low voltage(e.g., GND) and the signal SW2 having a high voltage (e.g., VDD) to theswitching circuit 240 after the set time period T1. In response to thesignal SW1 having the low voltage and the signal SW2 having the highvoltage, the transistor I2 may be disabled and the transistor I3 may beenabled to electrically decouple the voltage source 210 from the bitline BL and electrically couple the current sensor 220 to the bit lineBL. When the current sensor 220 is electrically coupled to the bit lineBL, the current sensor 220 may sense the current Tout through the bitline BL and the memory cell M. By sensing the current Tout after the settime period T1, inaccuracy in reading data due to parasitic couplingfrom the first pulse can be reduced or obviated.

In one approach, the timing controller 110 applies a signal SW1 having aset of second pulses to the transistor I2 of the switching circuit 240and a signal SW2 having a set of third pulses to the transistor I3 ofthe switching circuit 240. The set of second pulses and the set of thirdpulses may have a sampling period Ts with opposite phases. In oneexample, the capacitor C of the current sensor 220 may dischargeaccording to the current Iout through the bit line BL and the samplingperiod Ts. The sense amplifier of the current sensor 220 may sense thedecreased voltage at the capacitor C, and determine data stored by thememory cells, according to the amount of decrease in the voltage at thecapacitor C.

In one aspect, a falling edge of the signal WL applied to the split gateelectrode SG of the memory cell M through the word line is aligned witha rising edge of the signal SW1 and a falling edge of the signal SW2applied to the switching circuit 240. In one aspect, in response to thefalling edge of the signal WL, the memory cell M may be disabled fromconducting current. By aligning the falling edge of the signal WL withthe rising edge of the signal SW1 and the falling edge of the signal SW2applied to the switching circuit 240, the switching circuit 240 mayelectrically couple the voltage source 210 to the bit line BL andelectrically decouple the current sensor 220 from the bit line BL whenthe memory cell M is disabled, such that a fluctuation or variation in avoltage at the bit line BL, for example, due to the falling edge of thesignal WL through parasitic capacitances can be reduced.

Referring now to FIG. 10 , an example block diagram of a computingsystem 1000 is shown, in accordance with some embodiments of thedisclosure. The computing system 1000 may be used by a circuit or layoutdesigner for integrated circuit design. A “circuit” as used herein is aninterconnection of electrical components such as resistors, transistors,switches, batteries, inductors, or other types of semiconductor devicesconfigured for implementing a desired functionality. The computingsystem 1000 includes a host device 1005 associated with a memory device1010. The host device 1005 may be configured to receive input from oneor more input devices 1015 and provide output to one or more outputdevices 1020. The host device 1005 may be configured to communicate withthe memory device 1010, the input devices 1015, and the output devices1020 via appropriate interfaces 1025A, 1025B, and 1025C, respectively.The computing system 1000 may be implemented in a variety of computingdevices such as computers (e.g., desktop, laptop, servers, data centers,etc.), tablets, personal digital assistants, mobile devices, otherhandheld or portable devices, or any other computing unit suitable forperforming schematic design and/or layout design using the host device1005.

The input devices 1015 may include any of a variety of inputtechnologies such as a keyboard, stylus, touch screen, mouse, trackball, keypad, microphone, voice recognition, motion recognition, remotecontrollers, input ports, one or more buttons, dials, joysticks, and anyother input peripheral that is associated with the host device 1005 andthat allows an external source, such as a user (e.g., a circuit orlayout designer), to enter information (e.g., data) into the host deviceand send instructions to the host device. Similarly, the output devices1020 may include a variety of output technologies such as externalmemories, printers, speakers, displays, microphones, light emittingdiodes, headphones, video devices, and any other output peripherals thatare configured to receive information (e.g., data) from the host device1005. The “data” that is either input into the host device 1005 and/oroutput from the host device may include any of a variety of textualdata, circuit data, signal data, semiconductor device data, graphicaldata, combinations thereof, or other types of analog and/or digital datathat is suitable for processing using the computing system 1000.

The host device 1005 includes or is associated with one or moreprocessing units/processors, such as Central Processing Unit (“CPU”)cores 1030A-1030N. The CPU cores 1030A-1030N may be implemented as anApplication Specific Integrated Circuit (“ASIC”), Field ProgrammableGate Array (“FPGA”), or any other type of processing unit. Each of theCPU cores 1030A-1030N may be configured to execute instructions forrunning one or more applications of the host device 1005. In someembodiments, the instructions and data to run the one or moreapplications may be stored within the memory device 1010. The hostdevice 1005 may also be configured to store the results of running theone or more applications within the memory device 1010. Thus, the hostdevice 1005 may be configured to request the memory device 1010 toperform a variety of operations. For example, the host device 1005 mayrequest the memory device 1010 to read data, write data, update ordelete data, and/or perform management or other operations. One suchapplication that the host device 1005 may be configured to run may be astandard cell application 1035. The standard cell application 1035 maybe part of a computer aided design or electronic design automationsoftware suite that may be used by a user of the host device 1005 touse, create, or modify a standard cell of a circuit. In someembodiments, the instructions to execute or run the standard cellapplication 1035 may be stored within the memory device 1010. Thestandard cell application 1035 may be executed by one or more of the CPUcores 1030A-1030N using the instructions associated with the standardcell application from the memory device 1010. In one example, thestandard cell application 1035 allows a user to utilize pre-generatedschematic and/or layout designs of the memory system 100 or a portion ofthe memory system 100 to aid integrated circuit design. After the layoutdesign of the integrated circuit is complete, multiples of theintegrated circuit, for example, including the memory system 100 or aportion of the memory system 100 can be fabricated according to thelayout design by a fabrication facility.

Referring still to FIG. 10 , the memory device 1010 includes a memorycontroller 1040 that is configured to read data from or write data to amemory array 1045. The memory array 1045 may include a variety ofvolatile and/or non-volatile memories. For example, in some embodiments,the memory array 1045 may include NAND flash memory cores. In otherembodiments, the memory array 1045 may include NOR flash memory cores,Static Random Access Memory (SRAM) cores, Dynamic Random Access Memory(DRAM) cores, Magnetoresistive Random Access Memory (MRAM) cores, PhaseChange Memory (PCM) cores, Resistive Random Access Memory (ReRAM) cores,3D XPoint memory cores, ferroelectric random-access memory (FeRAM)cores, and other types of memory cores that are suitable for use withinthe memory array. The memories within the memory array 1045 may beindividually and independently controlled by the memory controller 1040.In other words, the memory controller 1040 may be configured tocommunicate with each memory within the memory array 1045 individuallyand independently. By communicating with the memory array 1045, thememory controller 1040 may be configured to read data from or write datato the memory array in response to instructions received from the hostdevice 1005. Although shown as being part of the memory device 1010, insome embodiments, the memory controller 1040 may be part of the hostdevice 1005 or part of another component of the computing system 1000and associated with the memory device. The memory controller 1040 may beimplemented as a logic circuit in either software, hardware, firmware,or combination thereof to perform the functions described herein. Forexample, in some embodiments, the memory controller 1040 may beconfigured to retrieve the instructions associated with the standardcell application 1035 stored in the memory array 1045 of the memorydevice 1010 upon receiving a request from the host device 1005.

It is to be understood that only some components of the computing system1000 are shown and described in FIG. 10 . However, the computing system1000 may include other components such as various batteries and powersources, networking interfaces, routers, switches, external memorysystems, controllers, etc. Generally speaking, the computing system 1000may include any of a variety of hardware, software, and/or firmwarecomponents that are needed or considered desirable in performing thefunctions described herein. Similarly, the host device 1005, the inputdevices 1015, the output devices 1020, and the memory device 1010including the memory controller 1040 and the memory array 1045 mayinclude other hardware, software, and/or firmware components that areconsidered necessary or desirable in performing the functions describedherein.

One aspect of this description relates to a memory system. In someembodiments, the memory system includes a memory cell and a bit lineconnected to the memory cell. In some embodiments, the memory systemincludes a pair of transistors to electrically couple, to the bit line,a selected one of: i) a voltage source to bias the memory cell and ii) asensor to sense a current through the memory cell. In some embodiments,the memory system includes a first transistor, where the firsttransistor and the bit line are connected between the pair oftransistors and the memory cell in series.

One aspect of this description relates to a method of operating a memorysystem. In one aspect, the method includes applying, by a memorycontroller, a first pulse to a memory cell. The first pulse has a firstedge at a first time and a second edge subsequent to the first edge at asecond time after the first time. In one aspect, the method includesapplying, by the memory controller in response to the first edge of thefirst pulse, a first voltage to a first transistor during a firstduration to electrically couple a voltage source to a bit line. Thefirst transistor may be connected to the memory cell through the bitline of the memory cell. In one aspect, the first duration is betweenthe first time and the second time. In one aspect, the method includesapplying, by the memory controller in response to the first edge of thefirst pulse, a second voltage to a second transistor during the firstduration to electrically decouple a sensor from the bit line. A sourceelectrode of the first transistor and a source electrode of the secondtransistor may be connected to the memory cell through the bit line ofthe memory cell. In one aspect, the method includes applying the secondvoltage to the first transistor during a second duration after the firstduration to electrically decouple the voltage source from the bit line.The second duration may be between the first time and the second time.In one aspect, the method includes applying the first voltage to thesecond transistor during the second duration to electrically couple thesensor to the bit line.

One aspect of this description relates to a memory system. In someembodiments, the memory system includes a set of memory cells and a bitline connected to the set of memory cells. In some embodiments, thememory system includes a first transistor connected between a voltagesource and the bit line and a second transistor connected between asensor and the bit line.

In one aspect, the memory system includes a memory controller connectedto the set of memory cell, the first transistor, and the secondtransistor. In one aspect, the memory controller is to enable the firsttransistor while disabling the second transistor to bias the set ofmemory cell according to the voltage source, and disable the firsttransistor while enabling the second transistor to sense a currentthrough the set of memory cell by the sensor. In one aspect, the memorycontroller is to apply a first pulse to the set of memory cell. Thefirst pulse has a first edge at a first time and a second edgesubsequent to the first edge at a second time after the first time. Inone aspect, the memory controller is to apply, in response to the firstedge of the first pulse, a first voltage to the first transistor duringa first duration to electrically couple the voltage source to the bitline. The first duration is between the first time and the second time.In one aspect, the memory controller is to apply, in response to thefirst edge of the first pulse, a second voltage to the second transistorduring the first duration to electrically decouple the sensor from thebit line.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A memory system comprising: a plurality of memorycells connected between a common bit line and ground; a pair oftransistors to electrically couple, to the bit line, a selected one ofi) a voltage source to bias at least a first one of the memory cells orii) a sensor to sense a current through the first memory cell, whereinthe pair of transistors are gated by respective pulse signals; and afirst transistor including: a first source/drain electrode connected toeach of the pair of transistors, and a second source/drain electrodeconnected to the bit line.
 2. The memory system of claim 1, wherein thepair of transistors include a second transistor and a third transistor,wherein a drain electrode of the second transistor is connected to thevoltage source and a source electrode of the second transistor isconnected to the first electrode of the first transistor, and wherein adrain electrode of the third transistor is connected to the sensor and asource electrode of the third transistor is connected to the firstelectrode of the first transistor.
 3. The memory system of claim 2,further comprising: a memory controller connected to the first memorycell and the pair of transistors, wherein the memory controller is to:enable the second transistor while disabling the third transistor tobias the first memory cell through the bit line according to the voltagesource, and disable the second transistor while enabling the thirdtransistor to sense the current through the first memory cell by thesensor.
 4. The memory system of claim 2, further comprising: a feedbackcircuit including an input connected to the second electrode of thefirst transistor that is connected to the bit line, and an outputconnected a gate electrode of the first transistor.
 5. The memory systemof claim 4, wherein the feedback circuit includes an operationalamplifier.
 6. The memory system of claim 4, wherein the feedback circuitincludes a fourth transistor including a gate electrode connected to thebit line and a drain electrode connected to the gate electrode of thefirst transistor.
 7. The memory system of claim 1, further comprising: amemory controller connected to the first memory cell and the pair oftransistors, wherein the memory controller is to: apply a first pulse tothe first memory cell, wherein the first pulse has a first edge at afirst time and a second edge subsequent to the first edge at a secondtime, apply, in response to the first edge of the first pulse, a firstvoltage to a second transistor of the pair of transistors during a firstduration, wherein the second transistor of the pair of transistors is toelectrically couple the voltage source to the bit line during the firstduration, in response to the first voltage, wherein the first durationis between the first time and the second time, and apply, in response tothe first edge of the first pulse, a second voltage to a thirdtransistor of the pair of transistors during the first duration, whereinthe third transistor of the pair of transistors is to electricallydecouple the sensor from the bit line during the first duration, inresponse to the second voltage.
 8. The memory system of claim 7, whereinthe memory controller is to: apply the second voltage to the secondtransistor of the pair of transistors during a second duration after thefirst duration, wherein the second transistor of the pair of transistorsis to electrically decouple the voltage source from the bit line duringthe second duration, in response to the second voltage, wherein thesecond duration is between the first time and the second time, and applythe first voltage to the third transistor of the pair of transistorsduring the second duration, wherein the third transistor of the pair oftransistors is to electrically couple the sensor to the bit line duringthe second duration, in response to the first voltage.
 9. The memorysystem of claim 7, wherein the first edge of the first pulse is alignedwith a rising edge of a second pulse applied to the second transistor ofthe pair of transistors.
 10. The memory system of claim 1, wherein thememory cells are each a flash memory cell.
 11. The memory system ofclaim 1, further comprising: a bias circuit to adjust a voltage at thebit line, the bias circuit including: another memory cell, and afeedback circuit to sense a voltage at the another memory cell andadjust a voltage at a gate electrode of the first transistor to controlthe voltage at the bit line.
 12. A method comprising: applying, by amemory controller, a first pulse to a memory cell, wherein the firstpulse has a first edge at a first time and a second edge subsequent tothe first edge at a second time after the first time; applying, by thememory controller in response to the first edge of the first pulse, afirst voltage to a first transistor during a first duration, wherein thefirst transistor is to electrically couple a voltage source to a bitline during the first duration, in response to the first voltage,wherein the first transistor is electrically coupled to the memory cellthrough the bit line of the memory cell, wherein the first duration isbetween the first time and the second time; and applying, by the memorycontroller in response to the first edge of the first pulse, a secondvoltage to a second transistor during the first duration, wherein thesecond transistor is to electrically decouple a sensor from the bit lineduring the first duration, in response to the second voltage, wherein asource electrode of the first transistor and a source electrode of thesecond transistor are electrically coupled to the memory cell throughthe bit line of the memory cell.
 13. The method of claim 12, furthercomprising: applying the second voltage to the first transistor during asecond duration after the first duration, wherein the first transistoris to electrically decouple the voltage source from the bit line duringthe second duration, in response to the second voltage, wherein thesecond duration is between the first time and the second time, andapplying the first voltage to the second transistor during the secondduration, wherein the second transistor is to electrically couple thesensor to the bit line during the second duration, in response to thefirst voltage.
 14. The method of claim 13, wherein the first edge of thefirst pulse is aligned with a rising edge of a second pulse applied tothe first transistor.
 15. The method of claim 12, wherein the memorycell is a flash memory cell.
 16. A memory system comprising: a set ofmemory cells connected between a common bit line and ground; a firsttransistor connected to a voltage source and coupled to the bit line; asecond transistor connected to a sensor and coupled to the bit line, asource electrode of the first transistor and a source electrode of thesecond transistor coupled to the bit line; and a third transistorconnected between each of the first and second transistors and the bitline, wherein the third transistor includes a first electrode connectedto each of the first and second transistors, and a second electrodeconnected to the bit line.
 17. The memory system of claim 16, furthercomprising: a memory controller connected to the set of memory cells,the first transistor and the second transistor, wherein the memorycontroller is to: enable the first transistor while disabling the secondtransistor to bias the set of memory cells according to the voltagesource, and disable the first transistor while enabling the secondtransistor to sense a current through the set of memory cells by thesensor.
 18. The memory system of claim 17, wherein the memory controlleris to: apply a first pulse to the set of memory cells, wherein the firstpulse has a first edge at a first time and a second edge subsequent tothe first edge at a second time after the first time, apply, in responseto the first edge of the first pulse, a first voltage to the firsttransistor during a first duration, wherein the first transistor is toelectrically couple the voltage source to the bit line during the firstduration, in response to the first voltage, wherein the first durationis between the first time and the second time, and apply, in response tothe first edge of the first pulse, a second voltage to the secondtransistor during the first duration, wherein the second transistor isto electrically decouple the sensor from the bit line during the firstduration, in response to the second voltage.
 19. The memory system ofclaim 18, wherein the set of memory cells is a set of flash memorycells, and wherein the memory controller is to apply the first pulse tothe set of flash memory cells through a word line connected between thememory controller and the set of flash memory cells.
 20. The memorysystem of claim 16, wherein the set of memory cells are each a flashmemory cell.